1. Field of the Invention
The present invention relates to technology for correcting the magnification deviation in a sub scanning direction in an image forming apparatus which performs image formation on recording paper based on a secondary transfer method using an intermediate transfer belt.
2. Description of the Related Art
With an image forming apparatus which performs image formation on recording paper based on a secondary transfer method using an intermediate transfer belt, there are cases where so-called magnification deviation occurs; specifically, an image of a size that is different from the scheduled size is formed on the recording paper due to the expansion and contraction of the intermediate transfer belt caused by temperature change or the like. For example, if the temperature of the intermediate transfer belt rises, the intermediate transfer belt will expand and the toner image transferred to the surface of the intermediate transfer belt will become stretched, and an image of a size that is larger than the manuscript size is formed on the recording paper.
In order to correct the magnification deviation, there is a conventional image forming apparatus which detects a sub scanning magnification error of a transfer transport device based on rate information of the transfer transport device, calculates a correction amount of the detected sub scanning magnification error, and performs control so as to change the drive rate of the transfer transport device in order to reduce the sub scanning magnification error based on the calculated correction amount.